The non-toxic pharmaceutically acceptable salts of certain tetrafluorophenethyl benzylamines are active anti-arrhythmic agents. A preferred agent of this class is .alpha.,.alpha.-dimethyl-4-(.alpha.,.alpha.,.beta.,.beta.-tetrafluorophene thyl)benzylamine isethionate. These benzylamines, their preparation and utility are disclosed in U.S. Pat. No. 3,812,177 issued May 21, 1974.
A novel monohydrate of .alpha.,.alpha.-dimethyl-4-(.alpha.,.alpha.,.beta.,.beta.-tetrafluorophene thyl)benzylamine isethionate has been discovered. This monohydrate can be readily converted to the anhydrous form for utilization in dosage forms. The process for preparing the monohydrate also offers a means of recrystallizing and/or purifying the isethionate salt from aqueous solution.